1. Field of the Invention
The present invention relates to a technique of accessing files in different networks.
2. Description of Related Art
Use of a call control protocol such as a SIP (Session Initiation Protocol) or a DDNS (Dynamic Domain Name System) allows communication terminals on different LANs (Local Area Networks) to directly carry out communications with each other via a WAN (Wide Area Network). Such a technique is referred to as a so-called VPN (Virtual Private Network). According to this technique, remote LANs can be used as if an interconnection is effected therebetween.
For example, use of the technique effects a connection between a LAN in a head office and a LAN in a branch office, so that terminals on the respective LANs can carry out communications with each other via the Internet.
There has been known a technique of allowing communication terminals on different LANs to carry out communications with each other via the Internet. According to this technique, the communication terminals on the different LANs log in to relay servers connected to the Internet via gateways so as to establish communication paths to the relay servers, respectively. Through the communication paths, the communication terminals can carry out communications with each other via the Internet. That is, this technique allows communications between LANs via relay servers on a WAN.
There has been also known a technique of allowing shared use of files in different LANs. For example, a file can be shared between LANs provided on different floors in an office building. That is, an office worker in one floor refers to a network shared folder to access a file in a LAN located on another floor.
As described above, conventionally, a file can be shared between different LANs. However, various problems must be solved in order to safely share the file between the different LANs via the Internet. That is, there arise many problems in terms of security when information about a shared file is referred to as it is over the Internet. In order to solve the problems, therefore, a new mechanism must be prepared.
In addition, there arise problems in terms of practical use because a LAN has no mechanism to dynamically send information about a shared file to another LAN. More specifically, in order to allow share use of a file via the Internet, a first LAN must provide to a second LAN information about the file to be shared. However, if a file is newly added or the file to be shared is deleted, the first LAN cannot dynamically send information about the addition or the deletion to the second LAN. In addition, LANs are fixedly connected to each other in a conventional VPN. Consequently, the VPN has no mechanism to respond to such a dynamic change that specific LANs share a specific file or folder as necessary.
Further, a current file sharing system has a problem of a poor referring property if there are many folders or files to be shared. More specifically, if many folders or files are listed, a user cannot readily find a target folder or file.